Two separate issues, both known about. The issue I mention is, I suspect, excessive clearance between the splines of the hubs and the output shafts. MMC solution is to pack with graphite grease (shaft only) however, this quickly proves to be a temporary solution as I can testify, regular attention is required.
Interestingly, I have undertaken quite a bit of research since originally raising this issue. It seems that vintage and classic racers use high temperature molybdenum infused grease on splined shafts / hubs. It is considered a better solution for heavy loads and higher temperatures. I sourced such a grease and spoke to the technical department of the manufacturer. Indeed they conclude that for the problem I have experienced a molybdenum based grease is a better solution. I procured some and removed the rear wheels (fourth time this season) and treated hubs and drive shafts with it. I will be undertaking a 250 mile trip next week and will report back. One thing I did notice on wheel removal and inspection (grease manufacturer instructed me to thoroughly clean all traces of graphite grease off hub and shaft prior to application of new grease) was evidence of galling between the back of the shaft and the outer radius of the hub. This suggests to me that a thin of grease is required between the two surfaces, which they now have.
